Hydrocarbon in fossil fuel, purified petroleum products and the like such as natural gas, liquefied natural gas, sour gas, crude oil, naphtha, heavy aromatic naphtha, gasoline, kerosene, diesel oil, gas oil, heavy oil, FCC slurry, asphalt, oilfield condensate, etc. often contains sulfur-containing compounds such as hydrogen sulfide and various —SH group-containing compounds (typically various mercaptans). The toxicity of hydrogen sulfide is well known, and in the industry that deals with fossil fuel and purified petroleum products, considerable costs and efforts are paid for reducing the content of hydrogen sulfide to a safe level. For example, for pipeline gas, a hydrogen sulfide content of not more than 4 ppm is required as an ordinary regulatory value. Hydrogen sulfide and various —SH group-containing compounds (typically various mercaptans) are volatile and therefore tend to emit in a vapor space, and in such a case, an offensive odor thereof is often problematic in the storage site and/or in the site around it and through the pipeline for use for transporting the hydrocarbon and the shipping system.
From the above-mentioned viewpoint, in a large-scale equipment that deals with fossil fuel or purified petroleum products, in general a system for treating hydrocarbon or hydrocarbon flow containing hydrogen sulfide is arranged. The system is equipped with an absorption tower filled with an alkanolamine, a polyethylene glycol, a hindered amine or the like to be kept in contact with hydrocarbon or hydrocarbon flow to absorb sulfur-containing compounds such as hydrogen sulfide and various —SH group-containing compounds (typically various mercaptans) and, as the case may be, carbon dioxide and the like.
On the other hand, use of a triazine for removing hydrogen sulfide from hydrocarbon has been known through the ages, but a triazine is defective in that it can be used only under a basic condition (as it decomposes under a neutral to acidic condition).
For removing hydrogen sulfide from hydrocarbon, using an aldehyde compound has also been proposed thorough the ages. Specifically, PTL 1 discloses reaction of an aldehyde compound and hydrogen sulfide, especially reaction of an aqueous formaldehyde solution and hydrogen sulfide in an aqueous solution having a pH range of 2 to 12. Following this, a large number of reports have been made relating to use of an aldehyde compound for removing hydrogen sulfide. For example, PTL 2 uses an aqueous solution of a water-soluble aldehyde such as formaldehyde, glyoxal or glutaraldehyde as an agent for removing hydrogen sulfide from hydrocarbon.
Merely adding a hydrogen sulfide remover in the form of an aqueous solution to hydrocarbon requires further improvement from the viewpoint of mixing them, and for example, PTL 3 says that, by adding an emulsifying agent such as sorbitan sesquioleate to the above aldehydes, the hydrogen removal efficiency can be improved. In PTL 4, for efficiently removing hydrogen sulfide from heavy oil, a hydrogen sulfide remover in the form of an aqueous solution and heavy oil are emulsified in an injection system equipped with a static mixer. In addition, there are known other examples of adding a polyalkylene glycol to a system for more increasing efficiency (PTLs 5 and 6).
In the case where the above-mentioned water-soluble aldehyde in the form of an aqueous solution thereof is used as a hydrogen sulfide remover, there is a risk of metal corrosion in the apparatus to be caused by the presence of an organic carboxylic acid in the aqueous solution as a result of oxidation of formaldehyde, glyoxal or glutaraldehyde. In particular, an aqueous solution of glyoxal has a strong metal corrosive property. From this viewpoint, PTL 7 and PTL 8 propose co-use of a phosphate salt such as LiH2PO4, NaH2PO4, Na2HPO4, KH2PO4, K2HPO4 or the like, a phosphate ester, a thiophosphate, a thioamine or the like as a corrosion inhibitor.
However, it is well known that formaldehyde is a mutagenic substance, and glutaraldehyde undergoes self-polymerization at a high concentration and therefore can be used only in a diluted state, and is therefore problematic from the viewpoint of volume efficiency.
On the other hand, PTL 2 discloses use of not only the above-mentioned water-soluble aldehyde but also acrolein having a higher organismic degree as a hydrogen sulfide remover, and in SPE Annual Technical Conference and Exhibition SPE146080 held in Denver, Colo. USA in Oct. 30 to Nov. 2, 2011, a report relating to hydrogen sulfide removal using acrolein as an active ingredient was announced. However, acrolein is a highly toxic compound and is therefore problematic in that the concentration thereof is strictly regulated from work safety and environment safety and that the compound requires careful handling.